Organic electroluminescent display device

ABSTRACT

The present invention overcomes image defects such as the brightness inclination or smears by reducing the line resistance of a power source bus line which supplies electricity to organic EL elements. A plurality of pixels which are arranged in a matrix array is connected to power source lines, and the plurality of power source lines are connected to a power source bus line. Both ends of the power source bus line are connected to a power source part via a FPC. By supplying electricity to both ends of the power source bus line from the power source part, the line resistance of the power source bus line can be reduced.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.11/710,944 filed on Feb. 27, 2007. Priority is claimed based on U.S.application Ser. No. 11/710,944 filed on Feb. 27, 2007, which claimspriority from Japanese application JP 2006-051235 filed on Feb. 27,2006, which is hereby incorporated by reference into this application.

Background

1. Field of the Invention

The present invention relates to an organic EL display device which usesorganic EL elements as pixels, and more particularly to an improvedpower source wiring which supplies electricity for allowing the organicEL elements to emit light.

2. Description of the Related Art

An organic EL element is a current-light-emitting-type element whichemits light when an electric current flows therethrough, wherein a largecurrent of several tens to 100 mA flows in a power source line in theinside of a TFT substrate on which the organic EL elements are formed.Particularly, in performing fixed-voltage driving of an EL displaypanel, when electricity is supplied to respective pixels via the powersource line in the inside of the TFT substrate from a terminal at aninlet of the display panel, due to a voltage drop which is generatedattributed to the resistance of the power source line, image defectssuch as the brightness inclination, smears and the like are generated.Accordingly, it is necessary to reduce the resistance of the powersource line in the inside of the TFT substrate (from the inlet of thedisplay panel to the respective pixels).

With respect to the reduction of the power source resistance, infollowing patent document 1, there is described a technique in which,for lowering a voltage drop attributed to the resistance of a drivepower source line which drives a plurality of organic EL elementsarranged in a matrix array, auxiliary power source lines are connectedto both ends (and an intermediate portion) of a drive power source line.

Patent document 1: JP-A-2003-108068

SUMMARY

In the above-mentioned patent document 1, although the voltage drop ofthe drive power source line which is connected to a plurality of organicEL elements is lowered, a voltage drop of the auxiliary power sourcelines which are connected to the plurality of drive power source linesis not taken into consideration.

Accordingly, it is an object of the present invention to provide anorganic EL display device which reduces a voltage drop of a power sourcebus line which supplies electricity to a power source line which isconnected to a plurality of organic EL elements.

The present invention is directed to an organic EL display device whichincludes a power source line which is connected to a plurality oforganic EL elements and a power source bus line which is connected tothe power source line, wherein electricity is supplied to a plurality ofportions including both ends of the power source bus line or both endsof the power source bus line.

According to the present invention, it is possible to obtain the organicEL display device which can reduce the voltage drop attributed to theline resistance of the power source bus line which supplies electricityto the power source line of the organic EL elements thus effectivelyovercoming image defects such as the brightness inclination, smears orthe like attributed to the power source bus line.

The display device according to the present invention is applicable to aTV receiver set, a PC monitor, a notebook type PC, a PDA, a mobilephone, a digital still camera, a digital video camera, a car navigationmonitor and the like. Further, the display device according to thepresent invention is also applicable to other self-luminouslight-emitting-type display.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general appearance view of an organic EL display deviceaccording to the present invention;

FIG. 2 is a drive circuit diagram of the organic EL display device of anembodiment 1 shown in FIG. 1;

FIG. 3 is a detailed view of a pixel made of an organic EL element shownin FIG. 2;

FIG. 4 is a drive circuit diagram of an organic EL display device of thesecond embodiment;

FIG. 5 is a drive circuit diagram of an organic EL display device of thethird embodiment;

FIG. 6 is a drive circuit diagram of an organic EL display device of thefourth embodiment;

FIG. 7 is a drive circuit diagram of an organic EL display device of thefifth embodiment;

FIG. 8 is a drive circuit diagram of an organic EL display device of thesixth embodiment; and

FIG. 9 is a drive circuit diagram of an organic EL display device of theseventh embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present invention is explained in conjunction withembodiments by reference to drawings.

Embodiment 1

FIG. 1A and FIG. 1B are general appearance views of an organic ELdisplay device according to the present invention, wherein FIG. 1A is afront view and FIG. 1B is a cross-sectional view. In FIG. 1A and FIG.1B, a pixel part 12 is formed on a TFT substrate (display panel) 11, andthe pixel part 12 is sealed by the TFT substrate 11, a sealing substrate13 which faces the TFT substrate 11, and a sealing material 14. In asealed space, for preventing the degradation of organic EL elements inthe pixel part 12 attributed to moisture, a desiccant material 15 issealed. Further, on the TFT substrate 11, a FPC (Flexible PrintedCircuit) 16 for supplying signal for driving the organic EL elements andfor supplying electricity from a power source part is mounted.

FIG. 2 is a drive circuit diagram of the organic EL display device shownin FIG. 1. In FIG. 2, pixels 22 each of which is formed of the organicEL element are arranged in a matrix array in a display region 21. Theplurality of pixels 22 are connected to power source lines 23 and theplurality of power source lines 23 are connected to a power source busline 24. Both ends of the power source bus line 24 are connected to apower source part 25 via the FPC 16. In this manner, the organic ELelements in the pixels 22 emit light with the electricity supplied toboth ends of the power source bus line 24 from the power source part 25.

Further, the plurality of pixels 22 which are arranged in a matrix arrayare connected to scanning lines 26 and data lines 27, and are driven inresponse to scanning signals of the scanning lines 26 selected by ascanning line drive circuit 28 and data signals from the data lines 27which are connected to a data line drive circuit 29.

A display control part 30 receives signals from the outside and suppliesthe scanning signals and the data signals to the scanning line drivecircuit 28 and the data line drive circuit 29 via the FPC 16 and, at thesame time, controls the power source part 25. Although the power sourcepart 25 and the display control part 30 are mounted on the FPC 16 in thedrawing, it is not always necessary to mount the power source part 25and the display control part 30 on the FPC 16.

Here, a cathode contact 31 is connected to cathodes of the organic ELelements in the pixels 22, wherein the cathode contact 31 is grounded tothe TFT substrate 11 and, at the same time, is grounded to the FPC 16via the FPC 16.

FIG. 3 is a detailed view of the pixels 22 each of which is constitutedof the organic EL element shown in FIG. 2. In FIG. 3, in each one of theplurality of pixels 22 arranged in the inside of the display region 21,a switching TFT 41 which is selected by the scanning line drive circuit28 and acquires the data signals from the data line drive circuit 29, acapacitance 42 which stores the data signals, and a driver TFT 44 whichdrives the organic EL element 43 in response to the data signals areprovided. The power source part 25 is connected to both ends of thepower source bus line 24.

The organic EL element 43 has an anode side thereof connected to thedriver TFT 44 and a cathode side thereof connected to a cathode currentline 45 which holds a reference potential (ground potential), and thecathode current line 45 is connected to the cathode contact 31.

In this embodiment, electricity is supplied from both ends of the powersource bus line 24 and hence, compared to the supply of electricity fromone terminal, it is possible to lower a voltage drop attributed to theline resistance of the power source bus line 24. By lowering the voltagedrop in this manner, it is possible to reduce the brightness inclinationin the horizontal direction of the horizontal power source bus line 24.Here, the brightness inclination in the vertical direction attributed tothe voltage drop of the vertical power source line 23 is ignored.

Embodiment 2

FIG. 4 is a drive circuit diagram of an organic EL display device of anembodiment 2 corresponding to FIG. 2 of the embodiment 1. Theconstitution which makes this embodiment differ from the embodiment 1lies in that electricity is supplied to a plurality of portionsincluding both ends of the power source bus line 24. Since otherconstitutions are substantially equal to the corresponding constitutionsshown in FIG. 2, the detailed explanation is omitted.

In FIG. 4, electricity is supplied to the plurality of portions (fiveportions) including both ends of the power source bus line 24 from apower source part 25 on the FPC 16 side. By supplying electricity to theplurality of portions in this manner, the line resistance of the powersource bus line 24 is divided thus achieving the substantial reductionof line resistance.

In this embodiment, compared to the embodiment 1, a voltage dropattributed to the line resistance of the power source bus line 24 can befurther lowered thus further reducing the brightness inclination.

Embodiment 3

FIG. 5 is a drive circuit diagram of an organic EL display device of anembodiment 3 corresponding to FIG. 2 of the embodiment 1. Theconstitution which makes this embodiment differ from the embodiment 1lies in that a drive circuit includes an upper power source bus line 51and left and right power source bus lines 52, 53. Since otherconstitutions are substantially equal to the corresponding constitutionsshown in FIG. 2, the detailed explanation is omitted.

In FIG. 5, one ends of a plurality of power source lines 23 areconnected to a lower power source bus line 24, and another ends of theplurality of power source lines 23 are connected to the upper powersource bus line 51. Further, the lower power source bus line 24 and theupper power source bus line 51 are connected with the left power sourcebus line 52. Further, the right power source bus line 53 may beconnected to the lower power source bus line 24 and the upper powersource bus line 51 so as to surround the display region 21 with thesepower source bus lines.

Electricity is supplied to both ends of the power source bus line 24from a power source part 25 on the FPC 16 side and, at the same time,electricity is also supplied to the upper power source bus line 51 viathe left power source bus line 52 (and the right power source bus line53). By supplying electricity from both ends of the power source line 23in this manner, it is possible to lower a voltage drop of the powersource line 23.

In this embodiment, along with the lowering of the voltage drop of thepower source bus line 24, the voltage drop of the power source line 23can be lowered and hence, the brightness inclination in the horizontaldirection can be reduced in the same manner as the embodiment 1 and,further, the brightness inclination in the vertical direction attributedto the line resistance of the power source line 23 can be also reduced.

Embodiment 4

FIG. 6 is a drive circuit diagram of an organic EL display device of anembodiment 4 corresponding to FIG. 4 of the embodiment 2. Theconstitution which makes this embodiment differ from the embodiment 2lies in, in the same manner as FIG. 5 of the embodiment 3, that a drivecircuit includes an upper power source bus line 51 and left and rightpower source bus lines 52, 53. Since other constitutions aresubstantially equal to the corresponding constitutions shown in FIG. 4,the detailed explanation is omitted.

In FIG. 6, electricity is supplied to a plurality of portions (fiveportions) including both ends of the power source bus line 24 from apower source part 25 on the FPC 16 side and, at the same time,electricity is also supplied to the upper power source bus line 51 viathe left power source bus line 52 (and the right power source bus line53). By supplying electricity to both ends of the power source line 23from the power source bus line 24 and the upper power source bus line51, a voltage drop of the power source line 23 is lowered.

In this embodiment, along with the further lowering of the voltage dropof the power source bus line 24, the voltage drop of the power sourceline 23 can be also lowered and hence, the brightness inclination in thehorizontal direction can be further reduced in the same manner as theembodiment 2, the brightness inclination in the vertical directionattributed to the line resistance of the power source line 23 can bealso reduced.

Embodiment5

FIG. 7 is a drive circuit diagram of an organic EL display device of anembodiment 5 corresponding to FIG. 5 showing the embodiment 3. Theconstitution which makes this embodiment differ from the embodiment 3lies in that a drive circuit includes an upper FPC 71 which supplieselectricity from both ends of the upper power source bus line 51. Sinceother constitutions are substantially equal to the correspondingconstitutions shown in FIG. 5, the detailed explanation is omitted.

In FIG. 7, a power source part substantially equal to a power sourcepart 25 on a lower FPC 16 side is provided to an upper FPC 71 side, andelectricity is supplied to both ends of the upper power source bus line51 from this power source part on the upper FPC 71 side. The lineresistance of the upper power source bus line 51 is reduced in the samemanner as a lower power source bus line 24. Here, a left power sourcebus line 52 and a right power source bus line 53 which connect the upperpower source bus line 51 and the lower power source bus line 24 may beomitted.

In this embodiment, compared to the embodiment 3, the brightnessinclination in the horizontal direction can be further reduced.

Embodiment 6

FIG. 8 is a drive circuit diagram of an organic EL display device of anembodiment 6 corresponding to FIG. 6 showing the embodiment 4. Theconstitution which makes this embodiment differ from the embodiment 4lies in that a drive circuit includes an upper FPC 71 which supplieselectricity to a plurality of portions including both ends of an upperpower source bus line 51. Since other constitutions are substantiallyequal to the corresponding constitutions shown in FIG. 6, the detailedexplanation is omitted.

In FIG. 8, a power source part substantially equal to a power sourcepart 25 on a lower FPC 16 side is provided to an upper FPC 71 side, andelectricity is supplied to a plurality of portions (five portions)including both ends of the upper power source bus line 51 from thispower source part on the upper FPC 71 side. The line resistance of theupper power source bus line 51 is reduced in the same manner as a lowerpower source bus line 24.

In this embodiment, compared to the embodiment 4, the brightnessinclination in the horizontal direction can be further reduced.

Embodiment 7

FIG. 9 is a drive circuit diagram of an organic EL display device of anembodiment 7 corresponding to FIG. 8 showing the embodiment 6. Theconstitution which makes this embodiment differ from the embodiment 6lies in that left and right power source bus lines 52, 53 are providedwith left and right FPCs 72, 73. Since other constitutions aresubstantially equal to the corresponding constitutions shown in FIG. 8,the detailed explanation is omitted.

In FIG. 9, a power source part substantially equal to a power sourcepart 25 on a lower FPC 16 side is provided to an upper FPC 71 and a leftFPC 72 (and a right FPC 73), and electricity is supplied to a pluralityof portions (five portions) including both ends of an upper power sourcebus line 51 and a left power source bus line 52 (and a right powersource bus line 53) from these power source parts. The line resistancesof these upper power source bus line 51 and left power source bus line52 (and right power source bus line 53) are reduced in the same manneras a lower power source bus line 24.

In this embodiment, the line resistances of the upper, lower, left andright power source bus lines can be reduced and hence, the brightnessinclination attributed to the power source bus lines can be reduced toextremely small values.

1. An organic EL display device comprising: a substrate having a displayregion; a flexible printed circuit connected to the substrate; and adrive circuit disposed on the substrate, wherein: the display regionincludes a plurality of pixels arranged in a matrix array, power sourcelines connected to the plurality of pixels, and data lines supplyingdata signals to the plurality of pixels, a power source bus line extendsalong a side of the display region and is connected to the power sourcelines, the power source bus line is arranged between the display regionand the drive circuit, electric power is supplied from a power sourcepart via the flexible printed circuit to a plurality of portions of thepower source bus line, and a cathode contact is connected to cathodes ofthe plurality of pixels, and cathode electrons are supplied from betweenan edge of the substrate and the power source bus line via the cathodecontact.
 2. An organic EL display device according to claim 1, whereinthe cathode contact is arranged opposite the power source bus line fromthe display region.
 3. An organic EL display device according to claim1, wherein the cathode contact is arranged between the power source busline and the drive circuit.
 4. An organic EL display device according toclaim 1, wherein the cathode electrons are supplied to the cathodecontact via the flexible printed circuit.